Aortic dissection generally is a catastrophic cardiovascular event which in the vast majority of patients is entirely preventable by proper treatment of systemic hypertension. Exactly how systemic hypertension is involved in the pathogenesis of aortic dissection is unclear, but it is clear that aortic dissection would virtually vanish if systemic hypertension disappeared. Patients with congenitally bicuspid aortic valves (with or without associated aortic isthmic coarctation), however, have an increased frequency of aortic dissection compared to individuals with three cuspid aortic valves, irrespective of the presence or absence of systemic hypertension. Most dissections involve the entire aorta. Those which stop within the aorta with or without a reentry site generally do so because of the extensive atherosclerotic plaques which may cause atrophy or degeneration of the underlying media, which is where the logitudinal dissection is located.